Electrostatic discharge clamp structures

ABSTRACT

A circuit structure includes: a network of clamps; sense elements in series with the clamps and configured to sense a turn-on of at least one clamp of the network of clamps; and feedback elements connected to the clamps to facilitate triggering of remaining clamps of the network of clamps.

FIELD OF THE INVENTION

The present disclosure generally relates to semiconductor structuresand, more particularly, to electrostatic discharge clamp structures andmethods of manufacture.

BACKGROUND

As semiconductor devices continue to scale downwards, e.g., shrink, thedesired spacing between features (i.e., the pitch) also becomes smaller.To this end, in the smaller technology nodes, devices become morevulnerable to external stress. Accordingly, it becomes ever moredifficult to fabricate devices with certain features to guarantee arobust chip due to critical dimension (CD) scaling and processcapabilities, as well as materials that are used to fabricate suchstructures.

Electrostatic discharge (ESD) events can cause issues, even for robustchips. For example, an ESD power clamp comprises distributed local clampnetworks which are implemented to provide protection from an ESD event.However, during an ESD event, some of the local clamps in the networksmay turn on first causing a snapback, i.e., be triggered, while otherclamps remain off. More specifically, in a conventional ESD event, aclamp will turn on and a snapback occurs at a certain point as thevoltage increases, resulting in a snapback to a lower voltage. Thisresults in a majority of the ESD current to flow only through thetriggered local clamps, causing an earlier failure of the device. Forexample, the snapback will cause a clamping of the ESD voltage below atriggering voltage, thereby causing a breakdown of the oxide materialbecause of the increase in triggering voltage. This requires an extradesign area to achieve the same ESD design target.

SUMMARY

In an aspect of the disclosure, a structure comprises: a network ofclamps; sense elements in series with the clamps and configured to sensea turn-on of at least one clamp of the network of clamps; and feedbackelements connected to the clamps to facilitate triggering of remainingclamps of the network of clamps.

In an aspect of the disclosure, a structure comprises: a network ofsilicon controlled rectifier (SCR) clamps; a passive element directlyconnected to at least one SCR clamp; a sensing amplifier directlyconnected to the passive element; and a triggering circuit connected tothe at least one SCR clamp to facilitate triggering of the at least oneSCR clamp.

In an aspect of the disclosure, a method comprises: sensing a currentdifference from a clamp in a network of clamps; and triggering remainingclamps in the network of clamps in response to a lack of currentdifference.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is described in the detailed description whichfollows, in reference to the noted plurality of drawings by way ofnon-limiting examples of exemplary embodiments of the presentdisclosure.

FIG. 1 shows an electrostatic discharge (ESD) protection circuit,amongst other features, and respective fabrication processes inaccordance with aspects of the present disclosure.

FIG. 2 shows a triggering circuit, amongst other features, andrespective fabrication processes in accordance with additional aspectsof the present disclosure.

FIG. 3 shows an implementation of the ESD protection circuit, amongstother features, and respective fabrication processes in accordance withadditional aspects of the present disclosure.

DETAILED DESCRIPTION

The present disclosure generally relates to semiconductor structuresand, more particularly, to electrostatic discharge clamp structures andmethods of manufacture. In embodiments, the structures herein includeelectrostatic discharge (ESD) sense elements and feedback elementsconnected in series with local clamps. During a triggering of a localclamp, a triggering circuit which includes sense elements and feedbackelements will feedback and facilitate the triggering of the remainingclamps in the network. Advantageously, the processes and structuresprovided herein allow for ESD protection without needing to enlarge eachindividual clamp.

The multi-triggering of the clamps is achieved by implementing ESD senseelements and a feedback network, amongst other features. In embodiments,the ESD sense elements can include a diode or resistor connected inseries with a local clamp and a detection circuit to sense the turn-onof the local clamp. Once the turn-on (triggering) of the local clamp issensed, the feedback elements facilitate triggering of any remaininglocal clamps in the network. In further embodiments, the feedbackelements can include a triggering circuit. Accordingly, by implementingthe circuitry here, all the clamps can be triggered allows for an evendistribution of an ESD current across all of the clamps in a network.Specifically, the triggering of all of the clamps allows for every clampto contribute in shunting the ESD current. In this way, the processesand structures provided herein utilize design space more efficientlysince enlarged clamps are not needed to provide adequate ESD protection.

The structures of the present disclosure can be manufactured in a numberof ways using a number of different tools. In general, though, themethodologies and tools are used to form structures with dimensions inthe micrometer and nanometer scale. The methodologies, i.e.,technologies, employed to manufacture the structure of the presentdisclosure have been adopted from integrated circuit (IC) technology.For example, the structures are built on wafers and are realized infilms of material patterned by photolithographic processes on the top ofa wafer. In particular, the fabrication of the structure uses threebasic building blocks: (i) deposition of thin films of material on asubstrate, (ii) applying a patterned mask on top of the films byphotolithographic imaging, and (iii) etching the films selectively tothe mask.

FIG. 1 shows a circuit and respective fabrication processes inaccordance with aspects of the present disclosure. More specifically,FIG. 1 shows a circuit 100 for protection from an electrostaticdischarge (ESD) event. The circuit 100 includes supply pins VDD and VSS,in addition to ESD sensing elements 130 a, 130 b, 130 c, which areconfigured to sense the triggering of a network of clamps, i.e., localclamps 150 a, 150 b, 150 c. Specifically, the sense elements, i.e., ESDsensing elements 130 a, 130 b, 130 c, are in series with the clamps,i.e., local clamps 150 a, 150 b, 150 c, and are configured to sense aturn-on of at least one clamp of the network of clamps, i.e., the localclamps 150 a, 150 b, 150 c.

The ESD sensing elements 130 a, 130 b, 130 c each comprise an element110 and a detection circuit 120 for sensing the triggering of localclamps 150 a, 150 b, 150 c. In embodiments, the element 110 can be apassive element directly connected to a clamp of the local clamps 150 a,150 b, 150 c. Particularly, the element 110 can be connected in serieswith the local clamps 150 a, 150 b, 150 c. In embodiments, the element110 can be a diode, as illustrated in FIG. 1 . In this way, the senseelements, i.e., the ESD sensing elements 130 a, 130 b, 130 c, comprisediodes. In alternative embodiments, the element 110 can be a resistor,amongst other examples of passive elements. Specifically, the senseelements, i.e., the ESD sensing elements 130 a, 130 b, 130 c, cancomprise resistors. In this way, the passive element, i.e., element 110,is a diode or a resistor. Further, the detection circuit 120 can be adifferential amplifier, amongst other sensing amplifiers. Specifically,the sensing amplifier is a differential amplifier. In this way, thesense elements, i.e., the ESD sensing elements 130 a, 130 b, 130 c,comprise a differential amplifier.

Still referring to FIG. 1 , the local clamps 150 a, 150 b, 150 c can besilicon controlled rectifier (SCR) clamps configured to prevent thebreakdown of circuitry. In this way, the local clamps 150 a, 150 b, 150c are a network of silicon controlled rectifier (SCR) clamps. Further, apassive element, i.e., element 110, is directly connected to at leastone SCR clamp of the local clamps 150 a, 150 b, 150 c. In even furtherembodiments, a sensing amplifier, i.e., the detection circuit 120, isdirectly connected to the passive element, i.e., element 110.

During an ESD event, an ESD current turns ON, i.e., triggers, at leastone of the local clamps 150 a, 150 b, 150 c by flowing into one or moreclamps of the local clamps 150 a, 150 b, 150 c. Triggering of a singleclamp, though, can result in a snapback and clamping of the ESD voltagebelow a triggering voltage, in an attempt to minimize a voltage drop. Toavoid such issues, the circuitry described herein prevents theoccurrence of the ESD current going through only a small number oftriggered clamps, while the remaining clamps remain OFF.

More specifically, to provide complete protection from the ESD event,circuit 100 is configured to turn ON all of the local clamps 150 a, 150b, 150 c during an ESD event in order to evenly distribute the ESDcurrent amongst all of the local clamps 150 a, 150 b, 150 c. In thisway, the ESD current will be distributed across all clamps, therebyeliminating the need for large clamps since all the clamps are nowutilized during the ESD event. Accordingly, by implementing thecircuitry herein, the size of the local clamps 150 a, 150 b, 150 c canbe reduced, e.g., from 3.5 amps down to 0.6 amps, for example. In thisway, each clamp is 0.6 amps.

In operation, the ESD sensing elements 130 a, 130 b, 130 c areconfigured to sense the triggering of any of the local clamps 150 a, 150b, 150 c during an ESD event. As an example, a diode, i.e., element 110,is turned ON when the local clamp 150 a is triggered, i.e., turned ON.The detection circuit 120 senses that the local clamp 150 a is triggeredby sensing a current difference between the element 110 and the localclamp 150 a when the local clamp 150 a is triggered. In this way, acurrent difference between the diode or the resistor, i.e., element 110,and at least one SCR clamp, i.e., the local clamp 150 a, is sensed bythe (sensing) differential amplifier, i.e., the detection circuit 120.Particularly, there is a sensing of a current difference between a clampin a network of clamps and a passive element. This current differenceresults in a determination that an ESD event is occurring. This sameprocess can occur for each of the remaining ESD sensing elements 130 b,130 c. For example, when the ESD sensing elements 130 b, 130 c sensethat their respective elements 110 are OFF, the detection circuits 120sense that the remaining local clamps 150 b, 150 c are OFF because nocurrent difference exists between the elements 110 of the remaining ESDsensing elements 130 b, 130 c and the remaining clamps 150 b, 150 c.

To prevent the ESD event from breaking down the circuitry (e.g., due toall of the local clamps 150 a, 150 b, 150 c not being ON), a feedbackelement 200 triggers any remaining clamps which are turned OFF, byinjecting currents into these clamps. In embodiments, the feedbackelements 200 comprise a triggering circuit to trigger any of the OFFclamps of the local clamps 150 a, 150 b, 150 c. In this way, atriggering circuit is connected to at least one SCR clamp to facilitatetriggering of the at least one SCR clamp. More specifically, thetriggering circuit can feedback and facilitate the triggering of any ofthe OFF clamps which have not been triggered. For example, after the ESDsensing elements 130 b, 130 c sense that the local clamps 150 b, 150 care not triggered, the feedback elements 200 will send a current intothe local clamps 150 b, 150 c. More specifically, there is a triggeringof remaining clamps, i.e., local clamps 150 b, 150 c, in the network ofclamps, i.e., the local clamps 150 a, 150 b, 150 c, in response to alack of current difference between the remaining clamps and remainingpassive elements, i.e., elements 110 of the ESD sensing elements 130 b,130 c.

The triggering of the remaining clamps 150 b, 150 c comprises injectingthe remaining clamps with a triggering current from a triggeringcircuit. In this way, all of the local clamps 150 a, 150 b, 150 c in thenetwork can now be triggered and can assist in shunting the ESD current.Specifically, the feedback elements 200 are connected to the clamps,i.e., the local clamps 150 a, 150 b, 150 c, to facilitate triggering ofremaining clamps of the network of clamps, i.e., the local clamps 150 a,150 b, 150 c.

FIG. 2 illustrates a feedback element 200 in accordance with aspects ofthe present disclosure. In embodiments, the feedback element 200comprises a resistor-capacitor (RC) triggering circuit for triggeringany of the OFF clamps. In this way, the triggering circuit is aresistor-capacitor (RC) triggering circuit. The RC triggering circuitincludes a load 210, a variable resistor R, diodes D1 and D2, a siliconcontrolled rectifier (SCR) 220, which is part of the local clamps 150 a,150 b, 150 c, and a capacitor C. In embodiments, power to the load 210is controlled by the SCR 220. For a positive cycle, the capacitor Ccharges to a trigger point of the SCR 220 in a time determined by an RCtime constant and a rising anode voltage. Further, varying theresistance through the variable resistor R controls a triggering orfiring angle of an input signal.

For a negative half cycle, the capacitor C charges in a reversedirection when a supply voltage increases towards a positive side and acapacitor voltage of the capacitor C recharges in an opposite direction.When the capacitor voltage reaches a threshold voltage, the SCR 220 willturn ON and the capacitor C will discharge through diode D2. Diode D1prevents the negative voltage between a gate and a cathode during thenegative half cycle. Activation of the SCR 220 will cause the localclamps 150 a, 150 b, 150 c to be triggered, i.e., turned ON. In furtherembodiments, other triggering circuits are contemplated which can injecta current into the local clamps 150 a, 150 b, 150 c.

FIG. 3 shows a schematic diagram 300 which implements the circuit 100 ofFIG. 1 . In a non-limiting illustrative example, the schematic diagram300 can meet industry ESD requirements, e.g., 2000V HBM, 250V CDM. Byway of example, a negative pulse 310 flows from supply VDD to groundGND. Further, a positive pulse 320 flows between VDD and theinput/output (I/O) and also into GND. In the event that an ESD current330 enters the I/O, the circuit 100 is able to provide ESD protection bytriggering all of the local clamps for even distribution of the ESDcurrent. In this way, the circuit 100 provides power pin ESD protectionbetween VDD and GND, and also provides I/O pin ESD protection betweenVDD and I/O and I/O and GND.

It should now be understood that the processes and resultant structuresdescribed herein will allow devices to be protected from electrostaticdischarge (ESD) events by evenly distributing the ESD current across allclamps. The distribution of the ESD current across all clamps isachieved by activating any remaining clamps which were not activated bythe ESD current. In embodiments, ESD elements in series with each clampsense the activation of the clamps. Once an ESD event is determined, theremaining clamps will be turned on by a feedback element. In this way,design space is utilized more efficiently because there is no need toenlarge a clamp, since all clamps contribute to shunting the ESDcurrent.

The method(s) as described above is used in the fabrication ofintegrated circuit chips. The resulting integrated circuit chips can bedistributed by the fabricator in raw wafer form (that is, as a singlewafer that has multiple unpackaged chips), as a bare die, or in apackaged form. In the latter case the chip is mounted in a single chippackage (such as a plastic carrier, with leads that are affixed to amotherboard or other higher level carrier) or in a multichip package(such as a ceramic carrier that has either or both surfaceinterconnections or buried interconnections). In any case the chip isthen integrated with other chips, discrete circuit elements, and/orother signal processing devices as part of either (a) an intermediateproduct, such as a motherboard, or (b) an end product. The end productcan be any product that includes integrated circuit chips, ranging fromtoys and other low-end applications to advanced computer products havinga display, a keyboard or other input device, and a central processor.

The descriptions of the various embodiments of the present disclosurehave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

What is claimed:
 1. A circuit structure, comprising: a network ofclamps; sense elements each respectively connected in series with acorresponding one of the clamps of the network of clamps; and feedbackelements each having an input connected to receive an input from atleast one of the sense elements and each having an output connected toat least one of the clamps, wherein the feedback elements each comprisea triggering circuit, the triggering circuit comprises a first inputconnected to an output of one of the sense elements, a second inputconnected to an output of an adjacent one of the sense elements and anoutput connected to at least two of the clamps.
 2. The circuit structureof claim 1, wherein the clamps are silicon controlled rectifier (SCR)clamps.
 3. The circuit structure of claim 1, wherein the sense elementscomprise diodes.
 4. The circuit structure of claim 1, wherein the senseelements comprise resistors.
 5. The circuit structure of claim 1,wherein the sense elements comprise a differential amplifier.
 6. Thecircuit structure of claim 1, wherein the triggering circuit is aresistor-capacitor (RC) triggering circuit.
 7. The circuit structure ofclaim 6, wherein each clamp is 0.6 amps, and the RC triggering circuitincludes a resistor coupled in series with a capacitor, a first diodecoupled in parallel with the resistor, a silicon controlled rectifier(SCR) coupled in parallel with the resistor and the first diode, and asecond diode coupled between a node connecting the resistor and thefirst diode and a control terminal of the SCR.
 8. The circuit structureof claim 1, wherein the sense elements comprise one of a diode and aresistor connected in series with the corresponding one of the clampsand a detection circuit to sense a turn-on of the corresponding one ofthe clamps.
 9. The circuit structure of claim 8, further comprising apassive element directly connected to at least one of the clamps and asensing amplifier.
 10. A circuit structure, comprising: a network ofsilicon controlled rectifier (SCR) clamps; a passive element connectedto at least one SCR clamp; a sensing amplifier connected to the passiveelement; and a triggering circuit comprising a first input connected toan output of the sensing amplifier, a second input connected to anoutput of another sensing amplifier adjacent to the sensing amplifier,and an output connected to the at least one SCR clamp and to at leastone other SCR clamp.
 11. The circuit structure of claim 10, wherein thepassive element is a diode or a resistor.
 12. The circuit structure ofclaim 11, wherein the sensing amplifier is a differential amplifier. 13.The circuit structure of claim 12, wherein a current difference betweenthe diode or the resistor and the at least one SCR clamp is sensed bythe differential amplifier.
 14. The circuit structure of claim 10,wherein the triggering circuit is a resistor-capacitor (RC) triggeringcircuit, and the RC triggering circuit includes a resistor coupled inseries with a capacitor, a first diode coupled in parallel with theresistor, an SCR element coupled in parallel with the resistor and thefirst diode, and a second diode coupled between a node connecting theresistor and the first diode and a control terminal of the SCR element.15. A method, comprising: sensing a current difference, via a sensingamplifier, between a clamp in a network of clamps and a passive elementconnected to the clamp; and triggering remaining clamps in the networkof clamps in response to sensing the current difference between theclamp and the passive element connected to the clamp, wherein thetriggering is performed by a triggering circuit comprising a first inputconnected to an output of the sensing amplifier, a second inputconnected to an output of another sensing amplifier adjacent to thesensing amplifier, and an output connected to the clamp and to at leastone other clamp of the network of clamps.
 16. The method of claim 15,wherein the sensing amplifier is a differential amplifier.
 17. Themethod of claim 15, wherein the passive element is a diode.
 18. Themethod of claim 15, wherein the passive element is a resistor.
 19. Themethod of claim 15, wherein the triggering the remaining clampscomprises injecting the remaining clamps with a triggering current fromthe triggering circuit.
 20. The method of claim 15, wherein thetriggering circuit is a resistor-capacitor (RC) triggering circuit, andwherein the RC triggering circuit includes a resistor coupled in serieswith a capacitor, a first diode coupled in parallel with the resistor,an SCR coupled in parallel with the resistor and the first diode, and asecond diode coupled between a node connecting the resistor and thefirst diode and a control terminal of the SCR.